I've found that the best thing is to sell Shards/Crystals/Clusters; to do that efficiently you need miner and botanist to 30; then whichever you want of those to 50, or both. Leveling up a crafting class, and desinthisys would also be smart as demi materia sells well on most markets and its level is dependent as far as I'm aware of your crafting skill for that class.